1. Field of the Invention
The present invention relates generally to a piezoelectric vibrating device utilizing a thickness shear vibration mode which is used as, for example, a piezoelectric resonator or a piezoelectric filter, and more particularly, to a piezoelectric vibrating device having a structure in which the production rate of ripples in a band is reduced by improving the shape of vibrating electrodes.
2. Description of the Prior Art
FIG. 2 shows one example of a conventional piezoelectric vibrating device utilizing a thickness shear vibration mode. The piezoelectric vibrating device 1 has a structure in which vibrating electrodes 3 and 4 are formed on both major surfaces of a piezoelectric substrate 2 having a rectangular plane shape which is subjected to polarization processing in the direction of an arrow P. The vibrating electrodes 3 and 4 are formed so as to be opposed to each other through the piezoelectric substrate 2 in a central region of the piezoelectric substrate 2. The vibrating electrode 3 is extended from one end 2a of the piezoelectric substrate 2 to the center, while the other vibrating electrode 4 is extended from the other end 2b of the piezoelectric substrate 2 to the center.
In the piezoelectric vibrating device 1, vibrating is excited in a region where the vibrating electrodes 3 and 4 are overlapped with each other by applying an AC voltage between the vibrating electrodes 3 and 4.
However, in the piezoelectric vibrating device 1 shown in FIG. 2, significant ripples are liable to be produced in a frequency region between the resonance frequency and the antiresonance frequency. More specifically, the production rate of the ripples is approximately 30 to 50%. The production of the above ripples is considered to be due to the non-uniformity of the shape of the vibrating electrodes 3 and 4. The vibrating electrodes 3 and 4 are applied by methods such as a method of printing and baking a conductive paste or a method of evaporating a metal material on the entire surface followed by etching.
In firing ceramics, however, a lot of pores appear on the surface of a sintered body. Accordingly, even if it is desired to form electrodes having a predetermined shape, the pores make it actually difficult to form electrodes having a uniform thickness and a desired shape. Further, in some cases, outer peripheral edges of the vibrating electrodes 3 and 4 may be blotted in printing or the edge portions may be irregular in etching. Furthermore, the edges of the vibrating electrodes 3 and 4 may be, in some cases, irregular by a cutting edge when the piezoelectric vibrating device 1 shown in FIG. 2 is cut down from a mother substrate.
More specifically, the above described ripples in the frequency region between the resonance frequency and the antiresonance frequency are considered to be due to the fact that the vibrating electrodes 3 and 4 are not formed in an exactly desired shape. Moreover, the deviation from the designed shape of the electrodes is not uniform. Consequently, the ripples are not produced in a uniform manner.